Seoul: Having more than five children increases the risk of Alzheimer's by 70 percent compared to women who have fewer children, a study has found. Researchers believe this may be because of the surge in levels of the hormone oestrogen towards the end of pregnancy.
They also found women who had an 'incomplete pregnancy' a miscarriage or abortion was half as likely to develop Alzheimer's later in life. The South Korean team claimed that oestrogen might offer a protective effect in the first few weeks of pregnancy, stimulating the brain.
The study was carried out on a total of 3,549 women in South Korea and Greece, who were tracked from the age of 71. The women provided information on their reproductive history including how many children they had had and miscarriages.
They also took tests of their memory and thinking skills to see whether they had developed Alzheimer's or its precursor, mild cognitive impairment. A total of 118 women developed Alzheimer's disease, and 896 women developed mild cognitive impairment, according to the study published in Neurology.
Women who had given birth to five or more children were 70 percent more likely to develop Alzheimer's disease than women who gave birth to fewer children. Of the 716 women with five or more children, 59 developed Alzheimer's, compared to 53 of the 2,751 women with fewer children.
The results stayed the same after researchers adjusted for other factors, such as other medical conditions, use of hormone replacement therapy and breastfeeding. Women who had experienced an incomplete pregnancy were about half as likely to develop Alzheimer's as women who had never had an incomplete pregnancy.
Of the 2,375 women who had an incomplete pregnancy, 47 developed Alzheimer's disease with a percentage of 1.9. This compared to 71 of the 1,174 women who never had an incomplete pregnancy, representing 6 percent.
On the tests of memory and thinking skills, women who had five or more children had lower scores than women who had fewer children. On a test where the maximum score is 30 points, and scores of 24 or more indicate normal thinking skills and scores of 19 to 23 indicate mild cognitive problems, the women with five or more children had average scores of about 22 points, compared to almost 26 points for the women with fewer than five children.
The researchers said a number of factors could be responsible including a huge surge in the hormone oestrogen, which may be protective in smaller doses but harmful in very large amounts. Other factors include the effects of having many children in employment and lifestyle.
The researchers said poorer people often had more children but that the study took these factors into account, and still holds true.
Dr. Ki Woong Kim of Seoul National University in Seoul, the study author, said: 'Oestrogen levels double by the eighth week of pregnancy before climbing to up to 40 times the normal peak level.' He added women who did not complete pregnancy might benefit from 'modestly raised levels of oestrogen.'
Dr. Doug Brown, chief policy and research officer at Alzheimer’s Society, said: ‘We know women are more at risk of developing dementia than men, but we don’t yet know why and as it’s the only one of the top ten killers we can’t treat or cure, research like this is vital to understand better what causes dementia and how we might be able to reduce that risk.
These researchers suggest that changing oestrogen levels during pregnancy may protect against dementia, but it’s a very complex relationship, and so far trials using hormone replacement therapy to tackle dementia have been inconclusive.
There are also limits in the way this data was collected, like not comparing people who’d been pregnant with people who hadn’t, making it tricky to fully understand how pregnancy and childbirth affect dementia risk.
This research shouldn’t give women who’ve given birth several times any cause for concern; it does highlight interesting links between changing hormone levels and dementia risk, but there are still too many unanswered questions. With dementia, the UK’s biggest killer, we’re investing in a broad range of research that will one-day beat dementia.
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